The present invention relates generally to imaging devices and more particularly to a device that aides placement and ensures accurate retention of documents on a platen of a flatbed imaging device.
Flatbed imaging devices including electrostatic and electronic document scanners and copiers, as well as multi function peripherals, typically require a face-down placement of media upon a transparent platen. An imaging assembly is typically positioned below the platen and is configured to obtain digital image data representative of an image represented on a sheet media. A transport assembly transports the imaging assembly in a plane substantially parallel to the plane of the platen. Image data includes data relating to the position and alignment of the media on the platen.
Flatbed imaging devices typically include a hinged platen cover that serves several purposes. The platen cover may serve both as a weight to hold the media as flat as possible and as an appropriately colored background for media that does not require the entire functional area of the platen. Additionally, the platen cover may include a document feeding mechanism for automatically feeding media onto the platen for automated multiple-document scanning.
A platen including a larger functional surface allows for scanning a wider range of original media, but an oversized platen may also present alignment problems when a user places curled, distorted, odd-shaped, small, multiple, or lightweight media on the platen. Curled, distorted, odd-shaped, small, multiple, or lightweight originals shift out of position easily.
Closing and opening the platen cover of a scanning machine may exacerbate the problem. Air turbulence caused by the two large flat planes of the platen and the platen cover can easily shift the position of the original media, whether during the closing of the platen cover for scanning or during opening for adjustment of the originals. This problem is particularly evident when scanning curled items like thermal facsimile papers, lightweight media such as receipts, or multiple smaller originals such as photographs or checks. FIGS. 1 through 3 illustrate the problems presented by flatbed imaging devices of the prior art.
Consequently, accurately scanning any media other than the most common sizes of originals requires tedious care and sometimes multiple readjustments to obtain a single useable image. This problem can result in inaccurate imaging, waste of operator time, waste of resources, and undue wear and tear on the imaging device.
Therefore, it may be advantageous to provide a simple and low-cost device that will easily hold any assortment or single piece of media, whether curled, distorted, odd-shaped, small, multiple, or lightweight, securely against the scanning or copying platen throughout the manual placement, scanning, and readjustment of the original media, and the opening and closing of the platen cover. It may also be advantageous to provide a method for retaining media against the platen in substantially the original placement in such a manner that the media does not shift prior to image processing. Additionally, there may be advantage in preserving an existing alignment of the media when the platen cover is opened for adjustment to the position of the media. The present invention consists of the combination and arrangement of parts hereinafter more fully described, illustrated in the accompanying drawings and more particularly pointed out in the appended claims, it being understood that changes may be made in the form, size, proportions and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.
The present invention is directed to a device for retaining media in a predetermined position for imaging. The present invention is further directed to a platen for a flatbed imaging device which includes an electrostatic charge that is imparted to the platen either passively or actively. The electrostatic charge occurs due to a movement of a charged object relative to the platen. In one embodiment of the invention, the electrostatic charge is imparted to the platen passively in the sense that the required charge is imparted by the placement of two materials exhibiting different triboelectric values in proximity to one another. In an active embodiment of the invention, the electrostatic charge is imparted to the platen actively in the sense that the requisite charge is imparted to the platen by the movement of a charge emitting device, such as a corona wire, in close proximity to the platen. The charge emitting device emits charged particles which are absorbed by the platen resulting in a charged platen surface.
In one embodiment of the invention, a flatbed imaging device includes a platen formed of a first insulator material having a first triboelectric effect value and a platen cover for the flatbed imaging device including an opposing insulator material having a second triboelectric effect value. An electrostatic charge is created on the surface of the platen by the relative movement of the opposing insulator material to the first insulator material of the platen. The action of opening and closing the platen cover provides the requisite relative movement to create and maintain a slight static electric charge on the surface of the platen. According to the invention, an associated electric field is created and maintained across the surface of the platen and material having a charge opposite the field will be attracted to the surface of the platen. The opposing insulator material may be incorporated with or integral to the platen cover.
This embodiment of the invention relies upon an electrostatic charge that occurs when two materials having disparate triboelectric characteristics are placed in position relative to one another permitting a transfer of electrons in what is characterized as a triboelectric transfer. When the materials are separated, a residual electrostatic charge remains on the surface of a material having lost electrons in the transfer.
The following is a list of materials arranged in series to show their relative position in a triboelectric series with the first materials being at the positive end of the series and the last materials being at the negative end of the series: air, glass, nylon, wool, silk, aluminum, paper, cotton (triboelectric value equal to zero), steel, hard rubber, nickel, copper, brass, silver, gold, platinum, acetate, rayon, polyester, styrene, orion, saran, polyurethane, polyethylene, polypropylene vinyl (PVC), teflon and silicone rubber. It should be recognized that the above list is provided for illustrative purposes only and that it is not intended that the listing be limiting in any sense as all materials exhibit a triboelectric value.
In general, materials at the upper end of the series tend to give up electrons freely during a triboelectric electron transfer resulting in a positively charged material. Conversely, materials at the lower end of the series tend to gain electrons freely during a triboelectric electron transfer resulting in a negatively charged material. It will be observed that cotton is positioned at a zero point in the series. Paper, the most common media is positioned prior to cotton in the series and exhibits a slight positive charge and a slight tendency to give up electrons. When paper is placed on glass that has been in contact with a material having a negative triboelectric value, the glass, having a greater positive charge than the paper, will attract the paper.
By way of illustration, when a platen cover including a hard rubber backing is placed in contact with a glass platen, and then removed, a residual positive static charge is created on the surface of the glass. Ideally, the media should be farther away in the triboelectric series to the material forming the platen than it is to the second insulator material of the platen cover. When such media is positioned on the glass, an attraction occurs between the glass and the media, tending to hold the media in a preselected position on the glass. This will cause an attraction to the platen rather than the platen cover.
In an alternate embodiment of the invention, the electrostatic charge is imparted to the platen actively by the movement of a charged corona wire relative to and in the proximity of the platen formed of a first insulator material.
A method for retaining media in a predetermined position for imaging on a flatbed imaging device may include the steps of imparting an electrostatic charge to a platen and electrostatically retaining the media in the pre-selected position on the platen for the imaging process. The electrostatic charge may be imparted passively or actively to the platen. The method is non-intrusive in that no marks or sticky residue from adhesive or cohesive fasteners are left on the platen. In one preferred embodiment of the invention, the glass platen may be coated or laminated with a clear plastic or polymeric film for increasing the static charge on the surface of the platen.